The present invention relates to automated apparatus for chemical testing of liquid samples to determine concentrations of substances therein, and more particularly to an improvement in liquid transfer means included therein.
The present invention is an improvement in chemical analyzers of the type in which sample liquid is taken from a sample container and aliquots thereof are each placed in one or more reaction containers. Reagents are added to each reaction container. A resulting reaction mixture is incubated, and then spectrophotometrically measured to indicate concentrations of substances in the samples for which the analysis is being conducted. In the preferred form, the present invention is included in a blood serum analyzer. An example of an automatic chemical testing apparatus of the sort contemplated by the present invention, is shown in U.S. Pat. Nos. 3,622,279 and 3,716,338, both to John J. Moran, and respectively issued on Nov. 23, 1971 and Feb. 13, 1973. These patents are commonly assigned to the assignee herein, and their disclosures are incorporated herein by reference.
In such chemical analyzers, sample liquid such as blood serum is provided in a source, such as a sample cup, and must be transferred to reaction containers. The same transfer means are used to transfer an amount of sample liquid from each of a number of successive samples to respective successive sets of reaction containers. If liquid remaining in the transfer means from a first sample is mixed with a next sample, intersample contamination, commonly referred to as carryover, may result.
Various prior art schemes have provided for transfer means which are subject to carryover. Common prior arrangements utilize pumping of sample liquid through tubes extending from a sample station to a reaction station. The transfer means in the above-cited patents to Moran is an improvement over those earlier forms of transfer means in that sample liquid is aspirated into a reservoir, and the reservoir is moved to reaction containers and becomes the dispensing means. The hydraulic pathlength through which the sample must travel is thus reduced, and far less surface area on the interior of conduits is provided on which sample liquid may remain. Further, efficient washing means are provided in the aspiration-dispensing means to guard against carryover.
The present invention comprehends further improvements in the transfer means for further improved reduction of carryover by positive displacement of sample liquid from the transfer means.